Things in Arcane are a bit confusing atm. There is a chance that the use of Invocation with a haste build will make it possible to continue the scorch weaving playstyle but if it happens Ghostcrawler said that they will change Invocation. I believe that Arcane Mages will be forced by Blizzard to play the "intended", less powerfull and boring rotation so Mastery will end up to be the priority stat. Everything need testing though...